Chip-classifying apparatus

ABSTRACT

According to the present disclosure, chip-classifying apparatus is provided with a platen having conductive film contacts in a configuration conforming to the contact configuration of the chip device to be classified. The platen is mounted at a test station and is electrically connected to suitable test apparatus. Motive means is provided for moving the chips to the test station and thereafter to a depository station. The motive means includes a tubular vacuum needle connected to a source of reduced pressure. A funnel is mounted to the open end of the vacuum needle, which funnel has a configuration and size conforming to that of the chip being moved so that the chip is oriented by reaction against the funnel to an orientation compatible with the contact configuration of the platen.

United States Patent 72] lnventor Mortimer Penberg Claremont, Calif. [21] Appl. No. 789,284 [22] Filed Jan. 6, 1969 [45] Patented Mar. 9, 1971 [73] Assignee Aerojet-General Corporation El Monte, Calif.

[54] ClllP-CLASSlFYING APPARATUS 12 Claims, 11 Drawing Figs.

[52] US. Cl 209/73, 209/81, 324/158, 339/95 [51] lnt.'Cl B07c 5/00 [50] Field of Search 209/73, 74, 81; 324/158, (Inquired); 339/95, (lnquired); 294/64 [56] References Cited UNITED STATES PATENTS 3,384,236 5/1968 Best et a1. 209/81 3,479,716 11/1969 Zanger Jr. et a1. 294/64(X) Assistant Examiner-Gene A. Church Attorneys-Edward O. Ansell and D. Gordon Angus ABSTRACT: According to the present disclosure, chip-classifying apparatus is provided with a platen having conductive film contacts in a configuration conforming to the contact configuration of the chip device to be classified. The platen is mounted at a test station and is electrically connected to suitable test apparatus. Motive means is provided for moving the chips to the test station and thereafter to a depository station. The motive means includes a tubular vacuum needle connected to a source of reduced pressure. A funnel is mounted to the open end of the vacuum needle, which funnel has a configuration and size conforming to that of the chip being moved so that the chip is oriented by reaction against the funnel to an orientation compatible with the contact configuration of the platen.

PATENIEUMAR 9.l97l v 3.568.831

sum 10F 2 Frd- 4 P/Q/ OR 1427' INVENTOR. Moer/Mze Pnvmes CHIlP-CLASSIFYING APPARATUS This invention relates to apparatus for handling chip devices, particularly during orientation and/or classification operations.

, The term chip device as used herein refers to any electrical device and/or circuit together with a plurality of electrical contacts integral therewith. Although the present invention will be described in connection with the handling of semiconductor chip devices, it is to be understood that the present invention may be utilized in connection with integrated circuit chips. Chip devices are commercially available on the order of about 20 to 50 mils. in length and width and about 1 to mils. thick. The chip deviceshave a plurality of electrical contacts integral therewith by which electrical and mechanical connection to the chip is made. Ordinarily, the electrical contacts are in the form of bead contacts, or bumps" as they are known in the art, beam lead contacts (which ordinarily extend beyond the periphery of the chip) or termination pads, and are ordinarily a thin layer of material deposited directly onto the surface of the chip and ordinarily have heights of a few thousand angstroms, which also make direct electrical and mechanical contact to the active device junctions.

Most chip-devices are active electrical devices whoseelectrical characteristics must be classified prior to being connected into an electrical circuit. Also, since most chip devices have more than two contacts, the orientation of the chip device with respect to a reference position must be known so that the chipdevice may be properly placed and bonded into the circuit.

Apparatus has been proposed for testing the electrical characteristics of chip devices. Ordinarily, such apparatus includes an aperture, or nest, sized to the chip which it will clas sify and has electrodes adapted to contact the contacts on the chip. Such apparatus, however, has not been capable of classifying chips having a different size than the chip for which the nest was designed. Thus, chips of various sizes and configurations had to be tested in special apparatus designed for the chip device. Also, apparatus as heretofore known, could not test chips having various contact patterns. Thus, test apparatus for classifying the electrical characteristics of chip devices have ordinarily been suited for a singletype of chip. Since chip classifying apparatus usually represents a substantial investment, it is desirable to provide apparatus capable of handling a wide variety of types of chips for classifying purposes so that various types of chips could be classified in one test machine, including facebonded or flip chip devices, beam lead devices, and conventional devices using termination pads as commonly employed in TO-type hermatically sealed or epoxy packages.

It is an object of the present invention to provide apparatus for handling chips for classifiers which is versatile so as to be able to handle any size or configuration chip as well as any size, type, or pattern of contacts.

Another object of the present invention is to provide apparatus capable of'handling a wide variety of chips for classifying purposes. i 1

Another object of the present invention is to provide apparatus for converting existing chip classifiers so as to enable such chip classifiers to handle and classify a wide variety of chips.

According to the present invention, a tubular vacuum needle having a funnel conforming to the configuration of the chip to be handled is provided for handling and moving such chips and for orienting them relative to the apparatus. A platen is providedwith a plurality of contacts having a configuration adapted to make electrical connection to the contacts of the chip. Both the vacuum needle and the platen are removable so that differently size vacuum needles may be utilized for differently sized chips, and different platens may be utilized for different contact configurations.

According to an; optional and desirable feature of the present invention; the platen is mounted on a resilient support so that chips disposed in a plane not perfectly aligned with the plane of the platen are-capable of being tested.

FIG. 5 is a side view in cutaway cross section taken along line 5-5 in FIG. 4;

FIG. 6 is a top view elevation of a platen for use in a classifier in accordance with the presently preferred embodiment of the present invention;

FIG. 7 is a side view in cutaway cross section taken along line 7-7 in FIG. 6;

FIG. 8 is a bottom planar view of a vacuum needle and fun- I nel taken along line 8-8 in FIG. 7;

FIG. 9 is a side view in cutaway cross section as in FIG. 7 with the platen in a different orientation;

FIG. 10 is a side view elevation, in cutaway cross section of a fragment of a platen contacting a chip contact; and

FIG. 11 is a side view elevation, in cutaway cross section of a fragment of a modification of a platen in accordance with the present invention, contacting a termination pad of a chip device.

In FIGS. 1 and 2 there is illustrated apparatus for handling chips during a classifying process; The apparatus generally comprises a substantially cylindricalhousing 10 adapted to rotate about axis 11 on shaft 12. Housing 10 supports a plurality of tubular vacuum needles 13 which are connected in fluid communication to a source .of reduced pressure, such as vacuum pump '14. Preferrably, valving means (not shown) is connected between needles l3 and pump 14 so as to control fluid communication between the pump and the individual needles during selected operations. Shaft 12 is driven by a suitable motive means, such as a motor (not shown). Also, means (not shown) is provided for reciprocally moving each needle 13 in a direction parallel to axis II, as shown by arrows 15 (see FlG. 2).

The apparatus illustrated in FIGS. 1 and 2 is capable of handling chip devices such as the flip chip 16 illustrated in FIG. 3. Chip 16 will ordinarily have a substantially square profile. Each side dimension d may be approximately 30 mils, and the thickness may be of the order of about 5 10 mils. It is to be understood that these dimensions may vary depending upon the chip device. Ordinarily, chip 16 is cut or broken out of a larger wafer by a suitable scribing and breaking method. This method results in the formation of the chip illustrated in FIG. 3, except that during the breaking of the wafer into the individual chips, the edges are usually not smooth and the dimensional characteristics may vary from chip to chip. As an alternative to the scribing and breaking method for forming the chips, the chips may be cut to form smoother sides and more uniform dimensions. By way of example, the chip devices may be cut in the manner described in copending ap-' plication Ser. No. 804,056 filed Feb. 28, 1969 for Cutting Apparatus by Joseph R. Camasta and assigned to the same assignee as the present invention.

The chip illustrated in FIG. 3 is a flip chip and has a plurality of contacts, or bumps 17 exposed on one planar surface thereof. The opposite planar surface is ordinarily relatively smooth. Contacts 17, which are known in the art as bumps, are ordinarily constructed of aluminum and provide electrical and mechanical connection for the particular chip device. For example, if chip 16 is a transistor, bumps 17 comprise the contacts for the base, emitter and collector of such transistor. Ordinarily, bumps 17 are approximately 6 to 10 mils. in diameter and 0.5 to 1.0 mils. in height. Ordinarily, there are three or more such bumps on each chip, but the number, pattern, size and location may very depending upon the type of chip. Some of the bumps may not provide electrical connection to the device and may be considered electrically dormant and are used for mechanical connection only.

Referring against again to FIG. 1 and 2, the apparatus for handling the chips, such as chip 16 illustrated in FIG. 3, further includes a feed mechanism 18 disposed on an inclined ramp 19. The feed mechanism and ramp are disposed relative to housing 16) to permit a supply of chips located in the feed mechanism to travel down ramp 19 in single order fashion. Sensing apparatus 20 is provided at the top of ramp 19 to reject and return to feed mechanism 18 all chips which do not have their contacts or bumps 17 properly aligned with respect to the apparatus. For example, if it is desirable that the bump contacts 17 be disposed downwardly with reference to FIG. 2, so that the planar surface of chip 16 will face a respective vacuum needle 13, sensor 20 will reject those chips whose contacts do not face into the plane of HG. 1 (downwardly in FIG. 2). At the bottom of ramp 19 is platform 21 where each chip comes to rest so that its bump contacts rest on the platform.

One of the vacuum needles 13 is moved downwardly from housing in the direction of arrow by means (not shown) until it comes into close relationship to the top planar surface of chip 16. The decreased pressure above the chip causes the chip to be drawn from platform 21 to be held by vacuum needle 13. Housing 10 then rotates to move needle 13 and the chip held by it to test platform 22.

The physical structure of the prior art test station 22 is illustrated in FIGS. 4 and 5. The prior test station comprised a plate 28 having a nest 29 formed therein. Nest 29 comprises shown). 30 through plate 28 having the same general configuration and size as chip 16. The sides 31 of aperture 30 are preferably tapered or inclined so that the top portion of the aperture is slightly larger than chip 16, while the bottom portion of aperture 30 is slightly smaller than chip l6. Disposed below nest 29 is a plurality of springloaded metallic contact levers 32. Levers 32 are arranged and disposed beneath the nest, so as to contact individual ones of bump contact 17 of chip 16. Levers 32 are connected by leads 33 to suitable test apparatus (not shown). By way of example, the test apparatus may comprise a computer adapted to sense the chips orientation and to measure the electrical characteristics of chip 16. One example of a suitable computer for testing chip 16 is a Teradyne Transistor Testor," commercially available from Teradyne Corporation.

In the operation of the apparatus thus far described, chip 16 is picked up by vacuum needle 13 from platform 21 and is moved by housing 10 to a position above test station 22. When positioned above test station 22, needle 13 moves the chip downwardly so as to place the chip in nest 29. If the chip is not rotationally aligned with nest 29, the tapered or inclined edges 31 of the nest cause the chip to rotate in the nest to a position as illustrated in FIG. 5. When in this position, bump contacts 17 press against respective spring-loaded lever contacts 32, thereby making electrical contact with such levers. The test apparatus (not shown) then operates through the lever contacts to test the electrical characteristics of the chip as well as sure its orientation.

The prior art apparatus as thus described, although providing relatively reliable testing of a particular chip, was not sufficiently versatile for testing other types of chips. The prior art apparatus was limited to the testing of chips having a particular size, configuration and bump contact height. If a chip 16 of a size smaller than the size of nest 29 was placed within the nest, the chip could be laterally displaced in the nest and there was no assurance as to proper orientation of the chip with respect to the apparatus. If a chip 16 which was too large for nest 29 was inserted in the nest, the chip would break and crumble within the nest and would leave particles which would obstruct other chips from being placed within the nest for test purposes. Another problem associated with such prior art apparatus was that the location, number and pattern of bump contacts on chips to be tested was limited because the classifier could not handle chips with various bump patterns, location and number. Since lever contacts 32 for contacting the bump contacts were extremely small in size, for example about 20 mils. wide, it was extremely difficult, if hot impossible, to relocate such lever contacts so as to test chips having other configurations of bump contacts. Furthermore if it was desirable to test chips having a greater number of bump contacts, more lever contacts had to be used, and the lever contacts would have to be even narrower than heretofore known, thereby increasing the difficulty of placement and alignment. Also, if the chip had a center bump contact encompassed by other peripherly disposed contacts, it was not possible to position a lever contact to test the center bump contact. Also, such prior art apparatus could not test chips having other types of contacts, such as beam lead contacts and conventional termination pad contacts. The present invention provides apparatus-handling chips of varying sizes and configurations so that such chips can be be classified by the apparatus.

In accordance with the present invention the classifying apparatus has a similar construction as illustrated in FIGS. 1 and 2. That is, chips 16 are picked up by tubular vacuum needles 13 and moved to the test platform 22, illustrated in FIGS. 1 and 2. The vacuum needles are connected to vacuum pump 14 and reciprocate in a direction parallel to axis 11, as heretofore described. However, at the test position, instead of having a nest with spring-loaded contact levers as heretofore described in connection to FIGS. 4 and 5, a single test platen 34 is provided, as illustrated in FIGS. 6 and 7. Platen 34 comprises a dielectric substrate 35 supporting a plurality of layers of metallic contact material '36. Contacts 36 are connected to the test equipment (not shown) by suitable wire 37 which is soldered or attached to the contacts 36. Contacts 36 are separated by a small distance, for example, about 3 mils. When the vacuum needle positions the chip over platen 34 so that electrical connection is made between bump contacts 17 and individual ones of contacts 36, the electrical characteristics of chip 16 may be tested and its orientation determined by a computer, such as a switching and sensing matrix.

To assure proper positioning (FIGS. chip 16 over the plate, the vacuum needle 13 can be provided with a funnel 38 having a configuration similar to the configuration of chip l6. Funnel 38 has incline walls which are, at the bottom, slightly larger than the largest dimensions of a chip 16. When the chip is picked up from platform 21, (FIGS. 1 and 2), the chips aligns itself by reaction against the walls of funnel 38 to fit snugly within the funnel. The reduced pressure within the funnel and within needle 13 holds the chip snugly within the funnel. In the event that a chip should be cocked or misaligned within the funnel, or if a chip of irregular configuration is attempted to be picked up, an air gap is formed between one edge of the chip and one surface of the funnel so as to permit air to enter the funnel thereby increasing the pressure therein, and preventing the vacuum needle from picking up the chip.

When vacuum needle 13 is moved to a position over platen 34, the vacuum needle moves downwardly to place chip 16 onto the platen so that bumps 17 contact separate metal contacts 36. The electrical characteristics of chip 16 may be tested and determined, and the orientation of chip 16 may be determined by the test equipment (a chip having four contacts, such as illustrated in the drawings, could be in any one of four orientations). If desired, the test apparatus can rotate the vacuum needle by an amount dependent upon the orientation of the chip so that the chip will be positioned in a preselected orientation for storage purposes.

After chip 16 has been classified at the test station 22, housing 10 rotates to move the vacuum needle 13 to a third position to deposit the chip into receptical 23. Receptical 23 may be any suitable type of storage apparatus, such as a magazine, adhesive tape, or may be a magnetic storage device, such as described in copending application Ser. No. 789,292 filed Jan. 6, 1969 for Chip Storage Apparatus" by Mortimer Penberg and Robert P. Mandal, assigned to the same assignee as the present invention. Ordinarily, the vacuum holding the chip is released, and pressure is sometimes applied to assure positive discharge of the chip from the needle 13.

It is possible when picking up chips with the vacuum needle having a funnel in accordance with the present invention, that some chips may be picked up at a slight angle to the plane normal to the axis of the needle. Hence, when brought down against a platen 34, the chip will be disposed in a plane different from that of the platen so that some of the bump contacts 1'7 may not contact the platen. For this reason, it is preferred that substrate 35 supported by resilient support 39, such as a small sheet of sponge rubber or a diaphragm. Hence, in the event that a cocked chip is brought against platen 34, the chip reacts against the platen which in turn reacts against the resilient support so as to cause the platen to assume the planar disposition of the chip, as shown in FIG. 9.

Many chips are provided with bumps 17 constructed of aluminum. Aluminum, being a good conductor and being a type of material easily'deposited in vapor deposition process, provides good electrical properties for flip chips. However, aluminum is susceptible of being oxidized when exposed to air, thereby forming aluminum oxide (A1 0 over the aluminum contact surface. The aluminum oxide is substantially an insulator which must be pierced or abrased before contact can be made. Heretofore, in the prior lever-type test stations, the abrasion or wiping action of the lever contact against the bump contact was sufficient to wearaway a sufiicient amount of aluminum oxide so as to make contact with the aluminum bump contact. However, when bringing the chip down by means of the vacuum needle directly onto the platen, as when using the apparatus according to the present invention, there is no assurance of an abrasion action between the bump contact and the metal forming the platen contact. For this reason, it is preferred to vapor or chemically deposit rhodium onto the surface of a coarse alumina substrate having A1 0 crystalites of sufficient height as to pierce the oxide over the aluminum contact surface. I

Referring to FIG. 10, the platen substrate 35 has alumina crystals 430 embedded therein. The exposed surface of the alumina crystals are covered with a layer of rhodium 41 to form the platen contacts. Although other metals my be used, rhodium is preferred because it provides good electrical conductivity and exhibits high resistance to wear. Bump contact 17 of the flip chip is shown contacting platen contact layer 41. Bump contact 17 comprises an aluminum body 42 and is shown as having an oxide coating 43 of aluminum oxide A1 0 formed thereon. As illustrated in FIG. when the bump contact contacts the rhodium covered alumina crystals rising from the mean surface of the contact layer, the crystals pierce the aluminum oxide coating over the aluminum of the bump contact, thereby making electrical contact between the aluminum material 42 and the rhodium plated contact 41. Hence, the oxide coating 43 is pierced by the rhodium covered alumina crystals to achieve electrical contact between the bump contact and the rhodium plated contact layer d1 of the platen. Other materials such as palladium or osmium may be used instead of rhodium.

With handling apparatus in accordance with the present invention, any desired chip may be handled, tested, and sorted by utilizing essentially the same apparatus. The vacuum needles and funnels are removable so that new needles and funnels may be utilized to accommodate other sizes, types and configurations of chips. The platen contact pattern may be formed by addition or subtraction thin-film deposition processes.

The platen is mounted at the test station and is used as herein before described. Of course, other platens may be constructed so as to test any type of chip to be tested.

In the event that the chip to be tested has termination contacts rather than protruding bump or beam lead-type contacts, it is desirable to form a bump on the platen contact, which bump would be constructed in the manner illustrated in FIG. ll. Thus, in the event that a flat pad contact becomes oxidized, the rhodium coated crystals of the substrate 35' are capable of piercing the oxide coating to assure electrical contact between the termination pad of the chipto be tested and the rhodium plated contact All illustrated in FIG. ill.

With the present invention, classifying apparatus is capable of handling and testing a variety of chips having various contact configurations, types and patterns as well as chips having various numbers of contacts. Furthermore, the utilization of the deposited platen contact and replaceable funnel and vacuum needles assures that the machine is capable of handling chips within ordinary dimensional tolerances. The chips may be of any particular configuration, such as square, rectangular, triangular, or even circular, and the type of chip contact may be any particular type, such as the extended beam type, the bump or merely flat termination pads. Hence, with the handling apparatus in accordance with the present invention becomes more versatile than previous classifiers. Furthermore, existing classifying apparatus can be converted in the manner herein described and incorporate the features of the present invention so as to be versatile.

This invention is not to be limited by the embodiments shown in the drawings or described in the description, which aregiven by way of example not of limitation, but only in accordance with the scope of the appended claims.

Iclaim:

1. In apparatus for classifying chip devices in accordance with their electrical characteristics which apparatus comprises a first station for supplying unclassified chip devices having a plurality of electrical contacts, a second station where such chip devices are to be classified, and a third station where the classified chip devices are deposited, and motive means for moving the chip devices between the first, second and third stations, the improvement comprising: an insulative substrate mounted at saidsecond station, a plurality of conductive film contacts on said substrate in spaced relation, said film contacts containing a plurality of crystals providing a rough surface on each film contact, said film contacts being so arranged and disposed and being so sized relative to the chip device contacts as to be capable of making electrical connection with individual contacts on the chip device, and means adapted to connect each of said film contacts to test apparatus.

2. Apparatus according to claim 1, wherein said motive means comprises a hollow needle adapted to be connected to a source of reduced pressure; and a funnel connected to a free end of said needle, said funnel having inclined walls in a configuration similar to the chip devices and being sized relative to the chip devices as to hold an individual chip device within said funnel, said funnel orienting each chip device relative to the substrate so that the chip contacts will make electrical connection with the film contacts.

3. Apparatus according to claim 2, wherein said substrate is mounted on a resilient support.

4. Apparatus according to claim 1 wherein said crystals are alumina crystals, and said film contacts comprises a layer of hard metal formed over the substrate.

5. Apparatus according to claim 2 having means supporting said substrate for aligning the substrate and the chip device into coplanar relationship.

6. Apparatus according to claim 1, wherein said substrate is mounted on a resilient support.

7. Apparatus according to claim 6, wherein said crystals are alumina crystals, and said film contacts comprises a layer of hard metal formed over the substrate.

8. Apparatus according to claim 7, wherein said layer of hard metal is a thin film of metal selected from the group comprising rhodium, palladium and osmium.

9. Apparatus according to claim 1, having means supporting said substrate for aligning the substrate and the chip device into coplanar relationship.

10. In apparatus for classifying chip devices in accordance with their electrical characteristics which apparatus comprises a first station for supplying unclassified chip devices having a plurality of electrical contacts, a second station where such chip devices are to be classified, and a third station where the classified chip devices are deposited, and motive means for moving the chip devices between the first, second and third stations, the improvement comprising: an insulative substrate having a plurality of conductive film contacts in spaced relation; resilient support means mounting said insulative substrate at said second station; said film contacts being so arranged and disposed and being so sized relative to the chip device contacts as to be capable of making electrical connection with individual contacts on a chip device; means adapted to connect each of said film contacts to test apparatus; said motive means comprising a hollow needle 'to be connected to a source of reduced pressure, and a funnel connected to the free end of said needle said needle having inclined walls in a configuration similar to the chip devices and being sized relative to the chip devices as to hold an individual chip device 

1. In apparatus for classifying chip devices in accordance with their electrical characteristics which apparatus comprises a first station for supplying unclassified chip devices having a plurality of electrical contacts, a second station where such chip devices are to be classified, and a third station where the classified chip devices are deposited, and motive means for moving the chip devices between the first, second and third stations, the improvement comprising: an insulative substrate mounted at said second station, a plurality of conductive film contacts on said substrate in spaced relation, said film contacts containing a plurality of crystals providing a rough surface on each film contact, said film contacts being so arranged and disposed and being so sized relative to the chip device contacts as to be capable of making electrical connection with individual contacts on the chip device, and means adapted to connect each of said film contacts to test apparatus.
 2. Apparatus according to claim 1, wherein said motive means comprises a hollow needle adapted to be connected to a source of reduced pressure; and a funnel connected to a free end of said needle, said funnel having inclined walls in a configuration similar to the chip devices and being sized relative to the chip devices as to hold an individual chip device within said funnel, said funnel orienting each chip device relative to the substrate so that the chip contacts will make electrical connection with the film contacts.
 3. Apparatus according to claim 2, wherein said substrate is mounted on a resilient support.
 4. Apparatus according to claim 1 wherein said crystals are alumina crystals, and said film contacts comprises a layer of hard metal formed over the substrate.
 5. Apparatus according to claim 2 having means supporting said substrate for aligning the substrate and the chip device into coplanar relationship.
 6. Apparatus according to claim 1, wherein said substrate is mounted on a resilient support.
 7. Apparatus according to claim 6, wherein said crystals are alumina crystals, and said film contacts comprises a layer of hard metal formed over the substrate.
 8. Apparatus according to claim 7, wherein said layer of hard metal is a thin film of metal selected from the group comprising rhodium, palladium and osmium.
 9. Apparatus according to claim 1, having means supporting said substrate for aligning the substrate and the chip device into coplanar relationship.
 10. In apparatus for classifying chip devices in accordance with their electrical characteristics which apparatus comprises a first station for supplying unclassified chip devices having a plurality of electrical contacts, a second station where such chip devices are to be classified, and a third station where the classified chip devices are deposited, and motive means for moving the chip devices between the first, second and third stations, the improvement comprising: an insulative substrate having a plurality of conductive film contacts in spaced relation; resilient support means mounting said insulative substrate at said second station; said film contacts being so arranged and disposed and being so sized relative to the chip device contacts as to be capable of making electrical connection with individual contacts on a chip device; means adapted to connect each of said film contacts to test apparatus; said motive means comprising a hollow needle to be connected to a source of reduced pressure, and a funnel connected to the free end of said needle said needle having inclined walls in a configuration similar to the chip devices and being sized relative to the chip devices as to hold an individual chip device within said funnel, said funnel orienting said chip device relative to said substrate so that the chip contacts will make electrical connection with the film contActs.
 11. Apparatus according to claim 10, wherein said substrate contains a plurality of crystals providing a rough surface for each film contact.
 12. Apparatus according to claim 11, wherein said crystals are alumina crystals, and said film contacts comprises a layer of hard metal formed over the substrate. 